The present invention relates to unlicensed wireless communications on vacant digital television (DTV) channels and, more particularly, to a method and system through which a wireless client device discovers vacant DTV channels.
Once the transition to DTV is completed in February 2009, proposed rules promulgated by the Federal Communications Commission (FCC) would permit wireless client devices to use for unlicensed communications DTV channels that are not used in a particular geographic area for DTV station or other primary user (e.g. licensed wireless microphone device) transmissions. Such vacant DTV channels are often referred to as White Space, and such wireless client devices are sometimes called White Space Devices, or WSDs.
To avoid interfering with primary user transmissions, a WSD must prior to transmitting discover which DTV channels are vacant, that is, what part of the local DTV broadcast spectrum is White Space. Such information is typically acquired by querying a remote primary user database using the WSD's known location and resolving a vacant channel list from the local DTV station and other local primary user information contained in the query response.
A common problem associated with vacant DTV channel discovery is that the WSD may not know its own location. One way for a WSD to discover its location is from the Global Positioning System (GPS). However, a WSD may not be equipped with a GPS receiver. Moreover, GPS receivers can suffer from poor indoor performance as coverage and reception within buildings is often severely restricted. Adding a GPS receiver to a WSD also may be considered overkill since a WSD does not need to know its location with GPS-like precision in order to determine which DTV channels in its vicinity are vacant. A location accurate within a few hundred meters will generally suffice.
Another way that a WSD might discover its location is Internet Protocol (IP) Geolocation. In IP Geolocation, a web server maps the source IP address in a received packet to a physical address of an organization that owns the IP address as listed in the American Registry for Internet Numbers (ARIN). However, this method for location discovery is error prone, as users of IP addresses owned by an organization often access the Internet from locations that are remote from the physical address of the organization registered with ARIN.